Cytologic differential diagnosis of follicular lymphoma grades 1 and 2 from reactive follicular hyperplasia: cytologic features of fine-needle aspiration smears with Pap stain and fluorescence in situ hybridization analysis to detect t(14;18)(q32;q21) chromosomal translocation.

Fine-needle aspiration cytology (FNAC) is a well-established technique for diagnosis of malignant lymphoma (ML). Generally, Giemsa but not Pap stain is used in FNAC. However, cytologic features obtained from Pap stain are also valuable. Very few studies on the cytologic characteristics of ML, as determined by Pap stain, are available. It is easier to observe nuclear irregularity and to identify nucleoli in ML cells by Pap stain than by Giemsa stain. Here, we applied Pap stain for cytomorphologic differential diagnosis of follicular lymphoma (FL) from reactive follicular hyperplasia (RFH). Eighteen biopsy-confirmed cases of FL grades 1 and 2, with available FNAC smears, and six cases of RFH were selected for this study. Low-power magnification showed well-known features, and tingible body macrophages and lymphoid cell aggregates were observed frequently in RFH and FL, respectively. In addition, the so-called two-nuclei-like cleaved cells were observed frequently in FL. These cells showed notably cleaved nuclei, and therefore, appeared to possess two nuclei. Under high-power magnification, the occurrence of cells with nucleoli >1 microm and of cleaved cells was high in FL compared to RFH. It is believed that FL derives from centrocytes and that FL cells are slightly larger than non-neoplastic small lymphocytes. However, analysis of cell diameter in this study indicated that small lymphoma cells were predominant in half the cases of FL grades 1 and 2, and the percentage of these cells was similar to that in RFH, showing why false-negative diagnosis of FL grades 1 and 2 occasionally occurs. There are limitations of FNAC in the diagnosis of FL. However, we believe that the appearance of two-nuclei-like cleaved cells and the high percentage of nucleoli-possessing cells, which we describe here, provide significant and valuable clues for the differential diagnosis of FL from RFH. Of 18 cases of FL grades 1 and 2, t(14;18)(q32;q21) was found in 13 cases with the use of destained FNAC smears. Our study suggests that, together with the cytomorphologic findings described earlier, FISH analysis for the chromosomal translocation, t(14;18)(q32;q21), is crucial for final cytologic diagnosis of FL grades 1 and 2.